1. Technical Field
The present invention relates to an image display medium, an image display device, a writing device and a displaying method, and in particular relates to an image display medium, an image display device a writing device, and a displaying method that display an image by the movement particles.
2. Related Art
Conventionally, display technologies such as Twisting Ball Display (rotational display by particles colored separately into two colors), or using electrophoresis, magnetophoresis, thermal rewritable medium, liquid crystal having memory function and the like have been proposed for a sheet-like image display medium which is repeatedly rewritable.
Among the above described display technologies, although thermally rewritable medium and liquid crystal having memory function are excellent in memory function for image, a color of its display surface cannot be made as white as white paper. Thus, it is difficult to confirm a distinction between image parts and non-image parts by means of visual observation in the case when a certain image is displayed, that is, there has been a problem of poor image quality. Other display technologies using electrophoresis or magnetophoresis are provided with memory function for image, and colored particles are dispersed in a white liquid. Thus, the display technologies using electrophoresis or magnetophoresis are excellent in white displaying. However, there has been a problem of poor image quality, since the white liquid enters between colored particles, black color forming image parts results in grayish.
Moreover, since white liquid is enclosed inside an image display medium, there is a possibility that the white liquid would leak outside the image display medium, if the image display medium is removed from an image display unit and handled roughly like paper. As another technology, a Twisting Ball Display has a memory function. Since inside an image display medium oil exists only in cavities around particles, but in a substantially solid state, it is comparatively easy to make the image display medium in the form of a sheet. However, even if each hemispherical surface of the particles has been coated in white and perfectly aligned at a display side, light entering between spheres of the particles is not reflected and is lost inside the display. Thus, in principle, a white display having a coverage of 100% cannot be achieved, and the color of the display results in slightly grayish appearance. Further, since a particle size is required to be smaller than a pixel size in order to obtain a high resolution, particles having different colors coated on must be made smaller, requiring a manufacturing technique of a high degree of precision.
A display technology, in which a conductive colored toner and white particles are contained in space between opposing electrode substrates, and electric charges are injected through a charge transport layer disposed on the inside surface of the electrode of a non-display substrate to the conductive colored toner, and an electric field between the electrode substrates causes charge-injected conductive colored toner to move toward a display substrate located facing the non-display substrate, and the conductive colored toner sticks to the inside of the display substrate, and contrast between the conductive colored toner and the white particles enables display of an image, was proposed as a display technology using a toner that solves such problems as mentioned above. The display technology is excellent in that the whole image display medium is made of solid matters and that display of white and black (color) can be completely switched in principle.
However, the above-described display technologies are in principle for achieving good two-color contrast, thus multi-color display of two or more colors requires separately driving pixels which are divided into segments such as CMY and RGB. Such dividing of pixels could reduce the display resolution to one third, even when the same number of pixels is used.